The present invention relates to an image sensor; and, more particularly, to a CMOS image sensor incorporating therein an optical layer for improving an optical efficiency thereof.
As is well known, an image sensor is an apparatus for receiving light, i.e., photons, reflected from an object and generating a digital image data. Especially, an image sensor made by a CMOS (complementary metal oxide semiconductor) fabrication technology is called a CMOS image sensor.
In FIG. 1, there is shown a cross-sectional view of a unit pixel contained in a conventional CMOS image sensor.
Generally, a unit pixel contained in the conventional CMOS image sensor is divided by a light sensing region 112 for accumulating photons reflected from an object and a peripheral circuit region 114 for transferring the photons to a data processing unit. A photodiode 120 is formed on top of the light sensing region 112 and transistors 130 are formed on top of the peripheral circuit region 114, to thereby provide a semiconductor structure.
For electrical isolation and electrical interconnection, a plurality of insulating layers 140, 150 and 160 and metal lines 152 and 162 are formed on the semiconductor structure. Then, a passivation layer 170 is formed on the uppermost insulating layer 160 in order to protect the unit pixel from an exterior.
However, the passivation layer and the insulating layers have been formed with consideration of electrical characteristic and device reliability rather than that of optical transmittance characteristic. As a result, an optical transmittance may be degraded due to a reflectance of the passivation layer and the insulating layers, thereby reducing sensitivity.
It is, therefore, an object of the present invention to provide a CMOS image sensor incorporating therein an optical layer for improving an optical efficiency thereof.
In accordance with an aspect of the present invention, there is provided a semiconductor image sensor for detecting a light incident thereto, comprising: a semiconductor substrate divided into a light sensing region and a peripheral circuit region; a photodiode formed on top of the light sensing region; at least one transistor formed on top of the peripheral circuit region; at least one insulating layer formed on top of the photodiode and the transistor; and an optical layer formed on the insulating layer to efficiently transmit the light to the photodiode.